This invention relates to the addition of alkyl groups to halides of silicon to produce more highly alkylated organosilanes. More particularly, this invention relates to an improved process for reacting organohalosilanes with organic halides in the presence of a halide-accepting metal.
In the silicones industry organosiloxanes are prepared from the hydrolysis of organohalosilanes. The predominant starting organohalosilanes are the diorganodihalosilanes which produce diorganopolysiloxane materials utilized in fluids, high-molecular weight linear polymers used in silicone elastomers, and the like. Organohalosilanes are primarily produced by the direct reaction of silicon and organic halides, as first disclosed by Rochow and his co-workers in the 1940's. The direct reaction can be controlled so that the predominant component is the diorganodihalosilane. However, other products of lower commercial value are also produced. These other products include tetrahalosilanes, organotrihalosilanes, and similar more highly halogenated species. It would be advantageous if such highly halogenated species could be efficiently converted to the more useful diorganodihalosilanes. Additionally, the demand for silanes of higher organic content such as triorganohalosilanes is often greater than the supply from the direct reaction.
As an early example of the preparation of organosilicon compounds using metallic reagents, Kipping and Dilthey both demonstrated the alkylation of tetrachlorosilane via reaction with an organomagnesium halide, the well-known Grignard process.
Hurd, J. Am. Chem. Soc. (1945), vol. 67, pp. 1545-1548, and Hurd, U.S. Pat. No. 2,403,370, issued Jul. 2, 1946, disclose the alkylation of tetrachlorosilane and various methylchlorosilanes by passing the vapors of these chlorosilanes together with an alkyl halide over finely divided aluminum, zinc, or other reactive metal at elevated temperatures, 300.degree. to 500.degree. C. Hurd discloses that a reaction occurs under these conditions in which chlorine groups on the chlorosilane are replaced by alkyl groups.
Straussberger et al., U.S. Pat. No. 4,155,927, issued May 22, 1979, discloses a process for preparing trimethylchlorosilane which comprises reacting methyldichlorosilane with methyl chloride and metallic aluminum in the presence of a diatomite. Straussberger et al. neither demonstrates nor suggests the instant invention in which the degree of methyl and chlorine exchange on silicon is maximized.
Turetskaya et al., Soviet Union Patent Publication SU 1162478, published Jun. 23, 1985, shows in examples that an alloy of aluminum with titanium in combination with silicon appears to affect the composition of the product of the reaction of methyl chloride and dimethyldichlorosilane. One cannot conclude that this is an improved catalyst.